How to find Indicated mean effective pressure?

A 4 stroke, single cylinder engine working on constant volume cycle, developes 7.5 KW brake power at 60 rev/sec the mechanical efficiency being 80%. The pressure at the begining of compression is 0.97 bar, the engine has a volumetric compression ratio of 7 and the maximum pressure reached in the cycle is 34 bar. If both compression and expansion is according to the law PV= costant where n=1.38, calculate Indicate Mean Effective Pressure ? 2. Relevant equations

indicated power = Pm x Lx A x N

3. The attempt at a solution

well i have tried different methods, but could`nt solve it, if anyone can help me with that ? i`ll b really gratefull. thanks.

the thing is that, there is no stroke or bore given in the question and if i use the volumetric compreesion ratio V1/V2 = 7 and put it in

P1V1^1.38 = P2V2^1.38

then i m getting nothing ? obvioulsy to calculate the Effective Pressure ( Pm ), bore or length of stroke should b known,
through the mechnical efficiney i got the indicated power !! but wat to do next ? kindly guide me.

well i had a very poor experience regarding this forum anyway i do like to leave one suggestion for the admin who r running this forum and that is kindly add one more thing in the topic " Why My Question Is Not Answered ? "

Its not necessary that admin can slove all the prbs, they r also not in full command of the subject.